1. Field of the Invention
This invention relates to a hematocrit measuring instrument, more particularly to an improved hematocrit measuring instrument capable of continuous measurement and capable of highly accurate measurement even in the case where there are variations in the concentration of the plasma electrolyte.
2. Description of the Prior Art
Measurement of the hematocrit of blood (the ratio of the volume of blood cells to the volume of the whole blood) is carried out as an effective technique in the diagnosis of diseases, medical treatment and health care. In view of the usefulness of this measurement there has been desired a better instrument for carrying it out.
Various instruments have been known for hematocrit measurement including those employing centrifugation, those which make the measurement from the blood cell count of a given volume (unit volume) of blood and the mean blood cell volume and those which make the measurement from the electrical resistance of the blood.
Among the hematocrit measuring instruments employing centrifugation, the type employing Wintrobe's method is generally considered to be standard. However, as this instrument performs the measurement using extracted blood specimens, it is not suitable for a system for carrying out measurements continuously.
The hematocrit measuring instruments which derive the hematocrit from the blood cell count and the mean blood cell volume are also unsuitable for carrying out measure continuously. More specifically, as they perform the measurement using diluted blood, if the concentration of the electrolyte and the protein in the diluted blood should differ from that in the blood plasma, the cell volume of the diluted blood will differ from the cell volume of the blood in the patient's body, thus giving rise to an erroneous measurement.
Although instruments which determine the hematocrit from the electrical resistance of the blood are convenient in that they afford a simple means of measurement, they are disadvantageous in that they are susceptible to error due to the changes in the resistivity of the plasma resulting from variations in plasma electrolyte concentration etc.